Hitherto, there has been known a patterning polarizing plate containing a plurality of polarization regions having different absorption axis directions, and there has been known that a light control device can be configured with use of two of the polarizing plate (e.g., Patent Document 1).
Specifically, the patterning polarizing plate contains a first polarization region having an absorption axis in a certain direction, and a second polarization region having an absorption axis in a direction orthogonal to the absorption axis direction of the first polarization region, and the first polarization region and the second polarization region are alternately arranged in a plane. Further, by disposing two of the above polarizing plates in parallel so as to face each other, a light control device can be formed.
In the light control device, two polarizing plates can be slid in a plane direction. Therefore, when the first polarization regions of two polarizing plates are overlaid on each other or the second polarization regions are overlaid on each other, or when the first polarization region of one polarizing plate is overlaid on the second polarization region of the other polarizing plate, brightness of light exiting the light control device can be adjusted.
That is, in a state in which the first polarization region and the second polarization region overlap (light blocking state), an absorption axis direction of the first polarization region is orthogonal to an absorption axis direction of the second polarization region. Therefore, theoretically, all of incident light from a side opposite to the viewing side of the light control device is blocked by the light control device, and the light does not reach the viewing side of the light control device. The incident light from the side opposite to the viewing side of the light control device is converted to specific linearly polarized light by a polarizing plate positioned on the side opposite to the viewing side (specific linearly polarized light is extracted from incident light). The linearly polarized light does not transmit through a polarizing plate positioned on the viewing side. Accordingly, light does not reach the viewing side of the light control device.
On the other hand, in a state in which the first polarization regions and the second polarization regions of two polarizing plates overlap (light-transmitting state), the absorption axis directions are parallel to each other. In this case, the incident light from the side opposite to the viewing side of the light control device is converted to specific linearly polarized light by a polarizing plate positioned on the side opposite to the viewing side, and the linearly polarized light transmits through a polarizing plate positioned on the viewing side. Accordingly, light reaches the viewing side of the light control device.
When the light control device is incorporated in a light-transmitting plate (e.g., window glass) requiring light control, a light control window can be formed. Since the light control window includes a light control device, it is possible to switch between a light-transmitting state and a light blocking state. Therefore, it is possible to moderately adjust a quantity of light entering the viewing side (e.g., indoor) of the light control window.
As described above, in the light-transmitting state, since specific linearly polarized light transmits through the light control device or the light control window, light reaches the viewing side of the light control device or the light control window. However, when the light control device or the light control window in the light-transmitting state is observed at the viewing side, color irregularities (difference in contrasting density) may be occurred between the first polarization region and the second polarization region. The color irregularities are occurred in response to a region configuration of the first and the second polarization regions. Therefore, for example, when the first and the second polarization regions are alternately disposed in the shape of a belt, a stripe-like pattern may appear. Occurrence of such color irregularities and a pattern resulting from the color irregularities has a problem of uglifying the light control device and the light control window. Particularly, the color irregularities are remarkable in observing the light control device or the light control window in an oblique direction on the viewing side.
[Patent Document 1] JP H09-310567 A